1. Technical Field
The present invention relates to a terminal relay device in a network.
2. Background Arts
SONET (Synchronous Optical NETwork)/SDH (Synchronous Digital Hierarchy) is known as the International Standards for a high-speed digital communication system employing an optical fiber, and is utilized for a backbone line of the Internet that establishes connections among Internet service providers. The SONET/SDH provides communication services using optical transmission levels based on OC-N (Optical Carrier N) such as OC-192, OC-48, OC-12, etc. Herein, OC-N, of which the basic unit is OC-1 (51.840 Mbps), is the SONET standard for specifying a transmission level given by an integral multiple (N-fold number) thereof. The term “SONET” is mainly used in North America. On the other hand, SDH is the standard (ITU standard) for Japan, Europe, etc. as the standard related to SONET. Both of the standards are called SONET/SDH.
Given as network applications on the SONET/SDH are a terminal configuration, a Linear ADM (Add Drop Multiplex) configuration, a UPSR (Uni-directional Path Switched Ring) configuration, a 2F-BLSR (Bi-directional Line Switched Ring) configuration, a 4F-BLSR configuration, and so forth.
FIG. 1 shows a network taking the terminal configuration. As in FIG. 1, the terminal configuration is that a point-to-point connection of terminal relay devices (which are also called ADX (Add Drop Cross-connect) devices) is established. In the terminal configuration, the terminal relay device supports a line redundancy function employing an APS (Automatic Protection Switch) adopting a 1+1 (one working traffic transmission path plus one protection traffic transmission path) configuration, etc.
In this terminal configuration, an interface card called an OC-N card is attached to a slot on a SONET/SDH side (which will hereinafter be referred to as a higher-level side) of each terminal relay device. This OC-N card is an interface that supports the OC-N (e.g., OC-48) transmission level given above.
As in FIG. 1, the terminal configuration involves employing one OC-N card for each of the working traffic and the protection traffic. Further, two lines of optical fibers F1, F2 are connected to the working traffic for transmitting and receiving. Similarly, two lines of optical fibers F3, F4 are connected to the protection traffic for transmitting and receiving.
This OC-N card is connected to an interface card (INF Card) to a low-order network (which hereinafter referred to as a lower-level side) connected to the SONET/SDH via a cross-connect processing circuit (XC card) and a line switch (Line SW) or a line bridge (Line BR). In this case, a transmission path extending from the lower-level side toward the SONET/SDH is called a transmission path in an add direction. Further, a transmission path extending from the SONET/SDH toward the lower-level side is called a transmission path in a drop direction.
Moreover, in the terminal configuration, signals from the lower-level side are transmitted from both of the working traffic transmission path and the protection traffic transmission path via, e.g., a line bridge 300. On the other hand, in signals received from both of the working traffic transmission path and the protection traffic transmission path, e.g., a line switch 301 selects a signal of the transmission path exhibiting a better transmission quality.
FIG. 2 shows a network taking the Linear ADM configuration. In the linear ADM configuration, three or more pieces of terminal relay devices (ADX devices) are linearly connected. FIG. 2 shows details of the terminal relay device (ADX device) located at an intermediate (relay) station on the link. In the Linear ADM configuration also, the terminal relay device performs route setting based on the add/drop function within the device, and performs at the same time a scheme for making the line redundant similarly to FIG. 1.
FIG. 3 shows a network taking the UPSR configuration. As shown in FIG. 3, the UPSR configuration is that the terminal relay device is connected to a ring network configured by two circuits of optical fibers F1-F4 and optical fibers F2-F3. In this type of ring-shaped network, in the two circuits, an interface existing on the left side as viewed from one terminal relay device is called an east-side (East) interface. Further, an interface existing on the right side as viewed from one terminal relay device is called a west-side (West) interface. The naming “the east-side” and “the west-side” is the naming for convenience in terms of simply distinguishing between the connecting directions but is not related directly to the actual geographical azimuth.
In the example in FIG. 3, the east-side OC-N card is connected to the optical fibers F1 and F2. Further, the signal is transmitted along the fiber F1 in a rightward circulating direction. Moreover, the signal is received along the fiber F2 in a leftward circulating direction.
Similarly, the west-side OC-N card is connected to the optical fibers F3 and F4. Further, the signal is transmitted along the fiber F3 in the leftward circulating direction. Moreover, the signal is received along the fiber F4 in the rightward circulating direction.
In the case of a high speed side line (OC-N) taking the UPSR configuration as shown in FIG. 3, signal channels allocated to communications between respective nodes (the terminal relay devices) on the system (ring network) are based on the transmission level represented by, e.g., STS-1 or OC-1, etc., wherein a line capacity for N-channels is built up on the whole.
On the card in charge of TSI (Time Space Interchange) within the device and a variety of protection switchover processes, for example, a lower-level side line (Tributary line) is subjected to line-setting in a higher-level side line (OC-N UPSR) direction. Namely, the lower-level side line is allocated with a line among the lines for (STS-1×N) channels on the UPSR network. This allocation process is called an add process.
On the occasion of this add process, the bridge 300 allocates the signals on the same line to both of the east side and the west side, whereby the signals on this line are transmitted along different routes on the ring network and the redundant configuration is thus actualized.
On the other hand, the signal receiving-side node (the terminal relay device) executes the line setting in a reversed direction (the higher-level side line→the lower-level side line) to the direction described above. In this case, the higher-level east- and west-side channels are extracted and allocated onto the lower-level side line.
Namely, the respective east- and west-side line signals that become termination target signals on the higher-level side line, are extracted. Then, the path switch 301 selects, on a path-level basis, the line exhibiting a better line quality from a detection state such as a path alarm etc. on the line.
By contrast, when the transmission path (line) is disconnected, etc., saving on a line-by-line basis is called line protection. Further, a switch used for the line protection and serving to switch over the working traffic line and the protection traffic line on the line-by-line basis, is called a line switch.
Note that a component (module) for branching off the signals into the working traffic line and the protection traffic line on the line-by-line basis is named a line bridge.
FIG. 4 shows a network taking a 2F-BLSR configuration. As shown in FIG. 4, in the 2F-BLSR configuration also, the terminal relay device, as in the case of the UPSR configuration, is connected to a ring network configured by two circuits of optical fibers F1-F4 and optical fibers F2-F3.
In the network based on the BLSR configuration, however, the terminal relay device (ADX device) does not transmit the same signal in the two directions on the east side and the west side when in transmission. If a fault occurs in the ring configuration using the two circuits (2 lines) of optical fibers, loopback (Bridge) control is executed on the line-by-line basis by use of OH (OverHead) bytes on an APS (Automatic Protection Switch) protocol, and the signal of the working cannel is shifted to a protection channel. With this scheme, the line saving is attained on the network taking the BLSR configuration.
FIG. 5 shows a network taking a 4F-BLSR configuration. In the 4F-BLSR configuration, the terminal relay device is connected to a ring network configured by four circuits (4 lines) of optical fibers. In the 4F-BLSR configuration, the terminal relay device executes, in the 4-fiber ring configuration, the line saving by 1+1 line protection and the line saving by a loopback operation on the line-by-line basis that employs the OH bytes on the APS protocol when both of the working traffic line and the protection traffic line are disconnected.
A main function of each of these terminal relay devices is the line setting (TSI) on the network. The line setting connotes a Through/Add/Drop process mapping onto an OC-N signal frame on the line-by-line basis. The terminal relay device employs (implements) a combination of functions corresponding to a variety of applications described above, and one single device is shared among the plurality of applications.
FIG. 5 shows an example of the network in which the higher-level side lines (OC-N) are configured by the 4F-BLSR. As describe above, the 4F-BLSR combines the 2F-BLSR configuration in which a half of the lines are allocated as the working traffic lines and the remaining half of lines are allocated as the protection traffic lines at a normal time with the 1+1 line protection/BLSR line saving.
The terminal relay device described above has interface cards (called OC-N cards) corresponding to the transmission levels (OC-N) on the network in a way that supports the variety of network applications. Further, this terminal relay device has a line setting (cross-connect) card, as a main component, provided with a variety of protection switchover functions.
FIG. 6 shows an example of a configuration of the terminal relay device implementing a plurality of protection functions. In FIG. 6, interface cards (INFcard#1-INFcard#n) are OC-N interface function units corresponding to the respective transmission levels on the higher-level side, or interface function units to the lower-level side lines.
These interface cards are, aiming at an OC-N transmission frame generating/terminating function, used as working (Work) channel/Protection (Protect) channel units when in the 1+1 redundant configuration, or east-side/west-side transmission units when in the ring configuration, or add/drop units on the lower-level side.
System blocks (Sys#1-Sys#n) provided in front and in rear of the cross-connect processing unit (XC) execute protection channel switchover corresponding to each of the variety of network applications by the line-setting. For example, the system block actualizes the line switchover process based on the APS protocol with respect to the transmission path (line) when in the 1+1 redundant configuration for the OC-N level transmission path. Moreover, the system block and the cross-connect processing unit configure a system capable of supporting the multiple applications by a line-setting (Add/Drop/Through) function.
In the configuration of the terminal relay device shown in the conventional example, however, the variety of protection channel switchover processing circuits and the cross-connect processing units are inflexible in their layout with respect to the corresponding interface cards.
Moreover, a line protection switchover circuit for switching over the working traffic and the protection traffic on the line-by-line basis and a path protection switchover circuit for switching over the working traffic and the protection traffic on a channel-by-channel basis, have hitherto been combined as a selector circuit.
Further, there has hitherto been a configuration in which the line protection switchover circuit, the path protection switchover circuit, etc. are arranged in series. For instance, a configuration in FIG. 6 is that a system block 310 for executing a Line APS process and a system block 311 for executing a BLSR process are connected in series.
In this configuration, when executing the Line APS process, the system block 311 for executing the BLSR process is set “Through”. Furthermore, when executing the BLSR process, the system block 310 for executing the Line APS process is set “Through”.
Thus, there has been adopted the configuration of sharing the (single) switchover circuit with the plurality of functions, or the configuration of establishing the in-series connection of the plurality of switchover circuits, and using one circuit while setting the other circuit “Through”. Such a configuration has a problem, wherein once the operation starts, the single switchover circuit is shared with the plurality of functions, and hence this switchover signal can not be changed independently of other functions. Then, there arises a problem that restriction is given to an in-device accommodating position (Slot) of the interface card connected to this switchover circuit and an upgrade method/function thereof.